Moldable material comprising asbestos and a cohydrolyzate of phenyl silicon trihalide and ethyl silicon trihalide



Patented Nov. 10, 1953 MOLDABLE-MATERIAL COMPRISING ASBES- TOS 'AND ACOHYDROLYZATE OF PHENYL SILICON 'TRIHALIDE AND ETHYL- SILICON TRIHALIDEAlfred Hirsch, Painesville, Ohio, assignor to Diamond Alkali Company,Cleveland, Ohio, a corporation of Delaware No-Drawing. Application May3, 1949, Serial No. 91,223

This invention relates to moldable resinous compositions comprisingsiloxanes, and moreparticularly relates to moldable resinouscompositions comprising siloxanes obtained from cohydrolyzates of aphenyl silicon trihalide and an ethyl silicon trihalide, in admixturewith inorganic filler material.

One of the objects of thepresent invention-is to provide heat-resistant,'moldable, resinous, siloxane-containing compositions suitable for usein structural applications and the like especially where high resistanceto flow of electric current is paramount, such as electrical instrumentpanel boards, electrical appliance grips, electrical insulators, and thelike. The compositions of the invention also have'application for usein'abrasive articles 'such'as grinding wheels, friction elements such asbrake linings, clutch facings, and the like.

Another object is to provide heat-resistant, resinous, moldable,siloxane-containing compositions of high tensile and flexural strength.

These and other objects will appear "from the description of theinvention'to be set forth more fully hereinafter.

It has long been known that siloxanes, comprising the condensedhydrolyzates of organosilicon halides or organo-halosilanes, aregenerally more heat-resistant than their chemical relatives in thefamily of thermosetting and thermoplastic resinous carbon compounds.Certain'of the siloxanes manifest'somewhat greater degree of heatresistance at elevated tempera- "tures than others. The siloxane resinsexhibit- :ing the highest degree of heat resistance are those obtainedfrom hydrolyzates of organosilicon trihalides. However, it hasheretofore been a disadvantage of these materials that they have beenextremely difficult to incorporate into molding compositions. Thisproblem has arisen largely from the general property of this group ofsiloxanes of having, in general, extremely short transient thermoplasticranges, due in part to the strong tendency of these hydrolyzates tocondense to insoluble, infusible masses during the preparation of themolding composition from the hydrolyzate of the appropriateorgano-silicon trihalides. As a result of the tendency of thesematerials to condense rapidly to insoluble, infusible masses, thesematerials have had limited application as moldable compositions, as themolded articles obtained therefrom are either very brittle, of lowtensile and fiexural strength, and for this reason of relatively limitedutility, or, because the condensation-of the hydrolyzates 8 Claims. (Cl.260-37) of these organo-silicon halides has advanced substantially tocompletion, comprise loose, porous, easily-friable masses, lacking anysubstantial degree ofcohesive strength.

A means for extending the transient thermoplastic range and of improvingthe tensile and flexuralstrength of a particularly useful heat-'-resistant siloxane obtainable from a cohydrolyzate of a phenyl silicontrihalide and an ethyl silicon trihalide is disclosed and claimed inapplicationSeraNo. 31,409, filed June 5, 1948, now abandoned. Themoldable compositions there described are characterized in part in thatthe siloxane portion of the compositions consists of a partiallycondensedcohydrolyzate of a mixture of to mol per cent of a phenylsilicon trihalide and 10 to 30 mol per cent of an ethyl silicontrihalide.

More particularly, the present invention includes resinous compositionscontaining partially condensed cohydrolyzates of a mixture of a phenylsilicon trihalide and an ethyl silicon'trihalide, combined with aninorganic filler selected from the group consisting of asbestos and amixture of asbestos with magnesium oxide.

The phenyl silicon trihalide and ethyl silicon trihalide compounds fromwhich the cohydrolyzates of the present invention are obtained may beany of several phenyl, or ethyl, silicon trihalides but arepreferablyphenyl and ethyl silicon. trichlorides, since these compounds aresomewhat more economically produced than the other halide derivatives,particularly the phenyl, or ethyl, silicon tribromide or triiodideandare more amenable to hydrolysis than the .phenyl silicon trifluorideor ethyl silicon trifluoride. In

the practice-of the present invention,-ethylsilicon-trihalide,preferably ethyl silicon trichloride, is mixedwitlnfor example, phenyl silicon trichloride to the extent of at least10 molper cent and preferably not more than 30 mol per cent of the totalmixture of the two silicon halide derivatives. Inraccordance with thedisclosure of the said co-pending application, Sen. No. 31,409, nowabandoned, it has been found that particularly satisfactory resultsmaybe .had when the preferred ethyl silicon 'tri'chlo'ride is present inthe mixture to the extent of to 25 mol per cent and a preferredcomposition, which has been found to be especially suitable in themanufacture of heat-resistant resinous compositions, is a combination of80 mol per cent of phenyl silicon trichloride with mol per cent of ethylsilicon trichloride. This preferred ratio of phenyl silicon trihalide toethyl silicon trihalide yields a cohydrolyzate material possessing asufficiently extended transient thermoplastic range to permit widevariations of conditions, such as temperature and acidity of thehydrolysis reaction mass, during the hydrolysis of the organo-siliconhalide mixture and during the subsequent heat-treating steps necessaryto obtain the partially condensed cohydrolyzate material in a solidcomminuted fusible form. It has been found that such varying conditionsduring the initial stages of the preparation do not adversely affect thefinal product and that a siloxane molding composition of sufficientlyextended transient range to yield a continuous solid mass when molded isobtained.

The partially condensed cohydrolyzates of a phenyl silicon trihalide andan ethyl silicon trihalide may be combined with the inorganic fillermaterials in the compositions of the present invention in any suitablemanner. For example, after the mixture of a phenyl silicon trihalide andan ethyl silicon trihalide, preferably the chlorides in solution in asuitable solvent, such as ethyl ether or isopropyl ether, has been addedto a mixture of ice and water in order to hydrolyze the silicon halidecompounds, and the cohydrolyzate of the organo-silicon halides in ethersolution has been recovered from the hydrolysis reaction mass, the othersolution of such cohydrolyzate may be added to a dry mass of asbestosfibers, or to a mixture of comminuted magnesium oxide and asbestosfibers.

Another method of combining the cohydrolyzates with the inorganicmaterials of the composition includes recovering the ether solution ofthe cohydrolyzate, as hereinabove described, evaporating the solventether therefrom. and recovering the partially condensed cohydrolyzate asa hard, fusible, solid material which may readily be comminuted to afine, light powder. Thereafter, the powdery cohydrolyzate may bemixed'with dry asbestos fiber or a mixture of asbestos fiber withcomminuted magnesium ox: ide.

The asbestos or combined asbestos and magnesium oxide may be employed inan amount ranging from 1:1 to 1:4 parts by weight of the hydrolyzate tothe asbestos or mixture of asbestos with magnesium oxide. A suitablesolvent, preferably a ketone, such as acetone or methyl ethyl ketone, isadded to the mixture in an amount sufficient to wet all of the dryingredients. Finally, the wetted mixture is kneaded in a mechanicalmixer, preferably one having a cutting and mixing action, such as aBanbury mixer or a Day mixer, and during such mixing, the small amountof solvent retained in the mixture may be driven off by indirectlyapplying heat thereto during the kneading operation. This procedureresults in a substantially dry composition in the form of relativelysmall agglomerates, which agglomerates may suitably be furthercomminuted in order to obtain the molding composition in powder form.

Thereafter, shapes may be obtained by molding the powdered moldingcomposition under heat and pressure, for example, at a temperature of250 to 350 F., and at a pressure of approximately 2000-4000 pounds persquare inch for a period of from one to two hours. After the moldingoperation has been completed, the molded shape may be removed from themold while hot and may suitably be subjected to further heating, forexample, at 475 to 550 F., for a period of 8-16 hours in order to effectthe final curing of the siloxane portion of the composition, i. e., toeffect the final substantially complete intermolecular condensation ofthe cohydrolyzate in the composition.

When employing asbestos fibers in the compositions of the presentinvention, it has been found that fibers of such length thatapproximately 75% of a given mass thereof are retained on a U. S.Standard No. 14 screen (12 mesh) give an especially strong tenaciouscured molded article.

When employing a mixture of magnesium oxide and asbestos in thecompositions of the present invention, suitable ratios of magnesiumoxide to asbestos fiber have been found within the range of 1:1 to 1:7.5parts by weight, preferably from 1:25 to 1:5 parts by weight.

The magnesium oxide comprising one of the preferred inert fillers may beused in any suit ably calcined, relatively fine form. Thus, material ofan average particle size to pass a 200 mesh screen is, in general,useful though materials of much finer particle sizes of the order of 50microns diameter or less may be used and are in general preferred. Thereappears to be no limit but practical considerations to the lower limitof particle size.

The asbestos of the compositions of the present invention, in additionto the fibrous form thereof described in some detail hereinabove, alsoincludes asbestos fibers generally in web form, such as asbestos paperor asbestos cloth. Where asbestos paper or cloth is used in thecompositions of the present invention, it has been found desirable todisperse the partially condensed cohydrolyzates in a suitable solvent,with or without the addition thereto of magnesium oxide, and to immersethe asbestos paper or cloth in the dispersion, and subsequently removethe solvent from the adhering dispersion prior to subjecting thethus-treated asbestos paper or cloth, either in the form of singlesheets or as laminates, to shaping by molding. Ordinarily, whenemploying a cohydrolyzate solution or dispersion containing 55% to 60%solids, the amount of dispersed material (solvent-free basis) adheringto the asbestos fiber or cloth varies from about 15% to about 40% of theweight of the paper or cloth, depending in part upon the densitythereof.

In addition to the ingredients above noted, it has been found desirable,in most molding compositions within the scope of the present invention,to accelerate the rate of intermolecular condensation, or rate of cure,as it is frequently referred to, of the partially condensedcohydrolyzate during the final heating step above described byincorporating in the solution of cohydrolyzate obtained from thehydrolysis reaction mass, a relatively small amount of an organic cureaccelerator, such as the mild organic bases, for example, the loweralkylol amines, specifically triethanolamine, diethanolamine,diethylamino ethanol, dimethylamino ethanol, propanolamine,dipropylamino propanol, and the like. In addition to these mild organicbases, certain heavy metal aesaeei salts of a crude" mixture oforganic-acids ex-' tracted from petroleum and known as n'aphthe'nic'acids, such as lead, cobalt, and manganese naphth'enates, and. 2'-ethyllead hexano'ate, a specific salt related to the general class of.naphthe nates, may also be employed as cure accelerators; Where cure'accelerators are employed in the compositions of the present invention,the cure time after molding may be decreased to about 4 to 6 hours.

In order that. those skilled inthe art may better understand the natureof the compositions o'i'the" presentinvention. and methods by which thesame may be obtained, the following specific example. is' offered:-

A mixture of organo-silicon trichlorides, containing 80 mol per cent ofphenyl silicon trichloride. and mol per cent of ethyl silicon.trichloride, is mixed with twice its volume of isopropyl ether and addedto a mixture of ice and water in excess of the amount required to clientthe hydrolysis of the organo-s-ilicon trichloride mixture. After thehydrolysis reaction has been completed, the solution of thecohydrol'yzate in isopropyl' etheris separated from the water-layer ofthe hydrolysis mass and dried by distilling a portion of the ether andsubstantially all of the water therefrom. There is obtained from thisdistillation a solution containing 57% of the partially condensedcohydrolyzate of phenyl silicon trichloride and ethyl silicontrichloride in isopropyl ether. This solution is then used to prepare aseries of compositions containing various amounts of asbestor fiber,characterized in part by the fact that approximately 75% of the fibersis retained on a U. S, Standard No. 14. screen (12 mesh), and magnesiumoxide of a light calcined variety having a particle size averaging 50microns in diameter or less. The inorganic portion of the compositionsis added to the ether solution of the cohydrolyzate and thereafter,triethanolamine is added to the mixture of inorganic filler andcohydroiyzate in the amount of 1% by weight of the amount of thecohydrolyzate in the composition. During the wet mixing of theingredients in a Banbury type mixer, the residual solvent isopropylether is evaporated from the mixture by admitting steam to the jacket ofthe mixer, the substantially solvent-free composition being obtained atthe end of the mixing period of approximately 10 minutes in the form ofsmall, solid agglomerates. The compositions in the form of softagglomerates of hydrolyzate and inorganic material are further dried byheating at approximately 195 F. in order to insure substantiallycomplete removal of the solvent. The compositions thus dried are thenpassed through a hammer mill in order to comminute the same to the formof very fine, light powders. Moldings are obtained by placing a suitableamount of these powders in a mold having a cavity of the desired shapefor the article finally to be obtained, and subjecting the moldingcomposition to a temperature of 350 F. at a pressure of approximately4000 pounds per square inch for one hour. The molded shapes are removedfrom the mold while still hot and subjected to further heating, forexample, at a temperature of 500-525 F. for a period of 2 to 3 hours inorder to complete the cure of the hydrolyzate portion of thecomposition.

A series of moldable compositions prepared in the detailed manner setforth immediately above and some; of the physical. properties of. suchcom-T positions are. set forth in' thetableb'elbw: The ingredients ofthe compositions are given inpercentages' byweight of the totalmixture;the-flexural. strength is given in pounds per square inch; and. theimpact strength is. given". in footpourrds. per inch. of notch.

"The cohydrolyzate prepared 'as noted at the beginning'ofi the example-Thecompositions of the present invention are found to have outstandingphysical properties; bothinthecombination of asbestos and hydro1y-- zatealone and the" combination with magnesium oxide. Moreover, in some waynot fully understood at the present. time, the magnesium:

oxide appears to have a specific advantageous erfeet over othergenerally similar, equally inert filler materials; such as finely groundsilicon dioxide in the form of"Cel ite, magnesium silicate in the formof vermiculite, barium sulfate, and the like;

Moreover, the compositions of the present invention have outstandingheat resistance while still maintaining their excellent properties to amarked extent at elevated temperatures of the order of 800 F. and forshort periods at much higher temperatures.

While there have been described various embodiments of the invention,the products described are not intended to be understood as limiting thescope of the invention as it is realized that changes therewithin arepossible and it is further intended that each element recited in any ofthe following claims is to be understood as referring to all equivalentelements for accomplishing substantially the same results insubstantially the same or equivalent manner, it being intended to coverthe invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. A moldable resinous composition containing a partially condensedhydrolyzate of a mixture of 70 to 90 mol per cent of phenyl silicontrichloride and 10 to 30- mol per cent of ethyl silicon trichloride tomake 100 mol per cent, and an inorganic filler material selected fromthe group consisting of asbestos and a mixture of asbestos withmagnesium oxide, said filler being present in an amount between 50% to80% of said composition.

2. A molded shape comprising a substantially cbmpletely intermolecularlycondensed cohydrolyzate of a mixture of 70 to mol per cent of a phenylsilicon trihalide and 10 to 30' mol per cent of an ethyl silicontrihalide to make mol per cent, and an inorganic filler materialselected from the group'consisting of asbestos and a mixture of asbestoswith magnesium oxide, said filler being present in an amount between 50%to 80% of said composition.

3. A molded shape comprising 20% to 50% by weight of a substantiallycompletely intermolecularly condensed cohydrolyzate of a mixtureof 70 to90 mol per cent of phenyl silicon trichloride and from 10 to 30 mol percent of ethyl silicon trichloride to make 100 mol per cent, and from 50%to 80% by weight of an inorganic filler material selected from the groupconsisting of asbestos and a mixture of asbestos with magnesium oxide.

4. A moldable resinous composition containing from 20% to 50% by weightof a partially condensed cohydrolyzate of a mixture of 70 to 90 mol percent of phenyl silicon trichloride and from 10 to 30 mol per cent ofethyl silicon trichloride to make 100 mol per cent, from 50% to 80% byweight of fibrous asbestos, 75% of which passes a 12 mesh screen.

5. A moldable resinous composition containing from to 50% by weight of apartially condensed. cohydrolyzate of a mixture of 70 to 90 mol per centof a phenyl silicon trichloride and from 10 to mol per cent of ethylsilicon trichloride to make 100 mol per cent, from to 80% by weight of amixture of asbestos with comminuted magnesium oxide having a particlesize such that substantially 100% of its particles will pass through a200 mesh screen.

6. A moldable resinous composition containing from 20% to 50% by weightof a partially condensed cohydrolyzate of a mixture of to 90 mol percent of phenyl silicon trichloride and from 10 to 30 mol per cent ofethyl silicon-trichloride to make 100 mol per cent, from 50% to 80% byweight of fibrous asbestos, of which passes through a 12 mesh screen,and magnesium oxide having an average particle size of less than 50microns.

7. A moldable resinous composition containing from 20% to 50% by weightof a cohydrolyzate of a mixture of '70 to 90 mol per cent of phenylsilicon trichloride and from 10 to 30 mol per cent of ethyl silicontrichloride to make 100 mol per cent, and from 50% to by weight ofasbestos web.

8. A moldable resinous composition containing from 20% to 50% by weightof a cohydrolyzate of a mixture of 70 to mol per cent of phenyl silicontrichloride and from 10 to 30 mol per cent of ethyl silicon trichlorideto make mol per cent, and from 50% to 80% by weight of a mixture ofasbestos web with magnesium oxide.

ALFRED I-HRSCH.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,258,222 Rochow Oct. '7, 1941 2,450,594 Hyde Oct. 5, 19482,460,795 Warrick Feb. 1, 1949 2,528,606 Pedersen Nov. '7, 1950 OTHERREFERENCES Plastics Catalog (1943), page 240.

1. A MOLDABLE RESINS COMPOSITION CONTAINING A PARTICALLY CONDENSEDHYDROLYZATE OF A MIXTURE OF 70 90 MOL PER CENT OF PHENYL SILICONTRICHLORIDE AND 10 TO 30 MOL PER CENT OF ETHYL SILICON TRICHLORIDE TOMAKE 100 MOL PER CENT, AND AN INORGANIC FILLER MATERIAL SELECTED FROMTHE GROUP CONSISTING OF ASBESTOS AND A MIXTURE OF ASBESTOS WITHMAGNESIUM OXIDE, SAID FILLER BEING PRESENT IN AN AMOUNT BETWEEN 50% TO80% OF SAID COMPOSITION.